The present invention relates to ball valves, and more particularly to a block-type ball valve which is designed to firmly retain the ball of the valve within the valve body.
As an example of conventional ball valves, a so-called "union-type ball valve" is known in which a ball is arranged in a cylindrical valve body in such a manner that it can open and close a fluid passage therein. Annular seals abut against the ball from both sides in the fluid passage, the annular seals being urged towards the ball by seal carriers. In the ball valve, when connecting sleeves are connected to the valve body, the connecting sleeves push the seal carriers towards the ball. The seal carriers are pushed by the connecting sleeves which are connected to the valve body, for instance, with union nuts, so that the abutment pressures of the annular seals to the ball can be adjusted by tightening or loosening the union nuts. Therefore, when the annular seals wear to the extent of causing leakage of fluid, the leakage can be eliminated by further tightening the union nuts.
The most serious drawback of a ball valve of this type is that, under the condition that the ball closes the fluid passage and the fluid pressured is applied, the union nut and the connecting sleeve on the other side cannot be removed. In order to repair or replace the pipe line connected to the connecting sleeve, it is necessary to loosen the union nut thereby to remove the connecting sleeve. However, if the connecting sleeve is removed, the ball and the seal carrier may blow out of the valve body due to the fluid pressure. Thus, the removal of the connecting sleeve under this condition is dangerous.
In order to eliminate this drawback, a ball valve, as disclosed by U.S. Pat. No. 3,550,902, for instance, has been proposed in which one seal carrier is provided on only one side of the ball while the other seal carrier is made integral with the valve body. With this valve, piping is performed with the seal carrier faced towards the side to which the pressure is applied. However, the ball valve is still disadvantageous due to the fact that the adjustment to compensate for wear of the annular seals is carried out by further tightening only one of the union nuts. If tightening is repeatedly carried out in this manner, the center of the ball will be significantly displaced from the center axis of the spindle. As a result, the torque required for turning the handle to turn the ball thereby to open and close the valve is increased; that is, the valve cannot be smoothly opened and closed. If the handle is forcibly turned, the spindle is pushed from one side only, as a result of which leakage occurs at the seals around the spindle.
U.S. Pat. Nos. 4,327,895 and 4,449,694 and Japanese Utility Model Application No. 105474/1982 disclose ball valves in which a seal carrier is screwed into the valve body in order to prevent the seal carrier from blowing out of the valve body. U.S. Pat. No. 4,059,250 discloses a valve ball in which a seal carrier having dogs along the periphery thereof is turned after being pushed into the valve body so that the dogs are engaged with lips formed in the bore at each end of the valve body in order to prevent the seal carrier from blowing out of the valve body. However, employment of the above-described methods of screwing the seal carrier into the valve body or turning the seal carrier after pushing into the valve body it is necessary to use a special tool. Furthermore, the ball valve becomes intricate in construction, and accordingly the valve assembly and disassembly operations are time consuming.
U.S. Pat. No. 3,807,692 discloses a ball valve which is formed by injection molding a valve body with synthetic resin, with pre-fabricated ball integrally with a spindle and annular seals in the mold cavity. In accordance with this method, because the ball is surrounded by the valve body, even when the connecting sleeve is removed by loosening the union nut, the ball cannot blow out of the valve body. However, the ball valve is still disadvantageous in that, since the annular seals together with the ball are insertedly molded in the valve body, further adjustment of the abutment pressures of the annular seals to the ball cannot be done, and if the annular seals are worn to the extent of causing leakage, uneconomically, the valve must be replaced in its entirety.